The modern internal combustion engine usually incorporates a pulley drive system for powering accessories driven by the engine crankshaft. The accessories typically include an air conditioning compressor, a power steering pump, a water pump, and an alternator. A front end accessory drive belt is trained around pulleys to supply power from the crankshaft of the engine to the accessories. The drive belt makes frictional contact with the face of the pulleys. The drive belt is most often a flexible reinforced polymeric belt.
Each of the accessories requires a driven pulley. In addition, operating a number of accessories, particularly with a serpentine drive belt, requires that the belt be handled carefully to allow placement of the belt in the locations needed to drive the accessories without slippage. Precise location of the belt frequently calls for the use of one or more idler pulleys.
Pulleys, such as idler pulleys, include a ball bearing (or other cartridge-type bearing) that is attached to the pulley either by press-fitting of the ball bearing into a pocket or by over-molding the ball bearing for retention. While common approaches, both of these operations may result in a distortion of the outer race of the ball bearing which may lead to irregular internal radial clearance of the bearing itself. Such distortion of the outer race is known to be a contributor to undesirable NVH issues while also reducing bearing durability.
Another undesirable result of the assembly process is that the average radial internal clearance of the bearing is changed during press fit or over-molding operations. As a consequence, the resulting radial internal clearance tolerance of the bearing cannot be controlled tightly after press fitting or over-molding.
As in so many areas of vehicle technology there is always room for improvements related to the design of a pulley for use in an internal combustion engine. Particularly, it would be advantageous to tightly control the radial internal clearance of the bearing so that bearing durability can be maximized and negative NVH effects minimized.